Condition responsive electric switch mechanism



Feb. 14, 1967 J. 1.. SLONNEGER 3,304,395

CONDITION RESPONSIVE ELECTRIC SWITCH MECHANISM Filed July 29, 1965 FIG] 4 Sheets-Sheet 1 FIG 2 INVENTOR JOHN L. SLONNEGER Y 2-H FM ATTORNEY Feb. 14, 1967 J. L. SLONNEGER 3,304,395

CONDITION RESPONSIVE ELECTRIC SWITCH MECHANISM S n i. 2 O

INVENTOR JOHN L SLONNEGER ATTORNEY Feb. 14, 1967 J. L. SLONNEGER CONDITION RESPONSIVE ELECTRIC SWITCH MECHANISM Filed July 29, 1965 4 Sheets-Sheet 5 INVENTOR JOHN L. SLONNEGER ATTORNEY Feb. 14, 1967 J. L. SLONNEGER CONDITION RESPONSIVE ELECTRIC SWITCH MECHANISM Filed July 29, 1965 4 SheetsSheet 4 INVENTOR JOHN L. SLONNEGER BY W ATTORNEY United States Patent 3,304,395 CONDITION RESPONSIVE ELECTRIC SWITCH MECHANISM John L. Slonneger, Morrison, 11]., assignor to General Electric Company, a corporation of New York Filed July 29, 1965, Ser. No. 475,820 Claims. (Cl. 200140) The present invention relates to electric switch mechanism and more particularly to automatic temperature control switches for use in connection with cooling devices, such as electric refrigerators and the like.

In refrigerating applications such as household refrigerator, freezer, and air conditioning units, condition responsive electric switch mechanisms are employed to control certain parts of the unit, for instance, the refrigeration cycle, in order to maintain the temperature at a selected location of the unit between predetermined upper and lower temperature limits. A typical switch mechanism includes a control knob for presetting the lever at which a condition responsive element, such as a thermally responsive bellows assembly, actu'ates the condition responsive contacts of the mechanism to effect the necessary control. The electric switch mechanism disclosed in the L. J. Howell Patent 3,096,419 issued July 2, 1963 is representative of this approach.

It is very desirable and advantageous in refrigerating applications to provide a condition responsive electric switch mechanism with auxiliary switch means which is also capable of selective control of additional refrigerating components or functions. For example, in a refrigera tion system, it is desirable that the switch mechanism can be independently employed to turn the motor-compressor component off and on. For air conditioning units, it is desirable to furnish selective control of the motor-compressor assembly and the ventilating fan so that they are independently operable.

Therefore, it is one object of the present invention to provide an improved condition responsive electric switch mechanism having condition responsive contacts and auxiliary switch means capable of selective operation.

Another object of the present invention is to provide an improved condition responsive electric switch mechanism having manually actuable contacts wherein the manually actuable contacts are controlled by the same means which is used for setting the level at which condition responsive contacts are actuated.

Briefly stated, in one form the present invention comprises a condition responsive electric switch mechanism which includes a pair of condition responsive switch contacts and an auxiliary switch means in the form of a pair of manually actuable contacts. A condition responsive element is used for controlling the operation of the condition responsive contacts and means are provided for varying the level at which the condition responsive contacts will be tripped. This means is also employed to trip the manually actuable contacts and by suitable operation of this means, selective control is effected of both the level at which the condition responsive switch contacts will trip as well as the auxiliary, manually actuable contacts.

Additional objects and advantages of the present invention together with a better understanding thereof may be had by referring to the following detailed description of the preferred embodiment of the present invention together with the accompanying drawings:

FIGURE 1 is a side elevational view of a condition responsive switch mechanism embodying the present invention;

FIGURE 2 is an end view of the insulating base of the switch;

- referred to as a cold control.

FIGURE 3 is a side elevational view partially in section and partially broken away along the line 33 of the switch of FIGURE 1;

FIGURE 4 is an exploded view showing the various parts of the switch of FIGURE 1 with the cover'assembly, the base, and the frame partially broken away;

FIGURE 5 is a sectional view of an alternate embodiment of the present invention;

FIGURE 6 is a top view of the switch of FIGURE 5; and

FIGURE 7 is a sectional view of still another embodiment of the present invention.

Referring now to FIGURE 1 there is shown a condition responsive switch mechanism which embodies one form of the present invention and which is generally The mechanism or switch 1 includes an insulating base 3 which may be formed of a molded thermosetting plastic, a U-shaped frame 5 which is formed of a suitable material such as stainless steel and which is securely mounted to the base 3, a bellows assembly 7 which is supported on the frame 5, and a cover assembly 9 which is used for closing the switch 1.

As can best be seen in FIGURES 2-3, the insulating base 3 serves as a mounting for three switch terminals 11, 13, and 15, the inner portions of which are contained within a generally U-shaped interval cavity 17 of the base 3. The terminals 11, 13, and 15 are fastened to the base 3 by staking and provide supports for a pair of relatively fixed contacts 19 and 23 and a pair of relatively movable contacts 21 and 25. It is noted that fixed contact 19 cooperates with movable contact 21 to form a condition responsive pair of contacts whereas fixed contact 23 cooperates with movable contact 25 to form a manually actuable pair of contacts in the switch. Movable contact 21 is mounted on a contact carrier 20, the free end 22 of which is engaged by an operating means, to be discussed more fully hereinafter, to cause movement thereof. Similarly, movable contact 25 is mounted on a contact carrier 24 which is engaged by an actuator, also to be discussed more fully hereinafter, to cause movement thereof. A closure member 26 provides a means for closing the switch from the atmosphere and thus keeps dust from collecting internally on the switch and interfering with the operation thereof.

As the switch is not easily discussed by separating the condition responsive portion from the manually actuable portion, reference is first made to the condition responsive switch.

In order to furnish a snap action operation of the condition responsive contacts 19 and 21, there is provided a U-shaped toggle spring 27 which is in continuous compression engagement between a pivot member 29 and a contact operating member 31 to continuously bias the contact operating member 31 such that the condition responsive contacts 19 and 21 are normally closed. For adjusting the biasing force of toggle spring 27, oppositely disposed channels 33 are molded into the base 3 and support pivot member 29 for sliding movement therein. To adjustably slide pivot member 29 within the channels 33, there is provided a differential adjusting screw 35 which engages the end flanges on the pivot member 29. Rotation of the differential adjusting screw 35, laterally moves the pivot member 29 to adjust the bias on the toggle spring 27.

Also included within the base 3 are a pair of stops 37 and 39 which are molded into the base 3 and provide means for limiting the movement of the contact operating member 31 between its open and closed positions so the biasing force provided by the toggle spring 27 is at all times within the most desirable range of the spring potential.

The frame 5 of the switch is generally U-shaped and has a pair of oppositely disposed symmetrical legs 41 connected by a bight 43 as is best seen in FIGURE 4. Each of the symmetrical legs 41 includes a specially configured slot 45 and inwardly bent upper 47 and lower tabs 49 which provide means for connecting and supporting the frame 5 of the insulating base 3. The insulating base 3 is provided with a pair of specially configured oppositely disposed ears 51 over which the slots 45 of the U-shaped frame fit for connection thereto.

In order to efficiently operate the condition responsive contacts of the switch 1, contact operating member 31 is pivotally supported in the frame 3 by providing inwardly turned tabs 51 which extend through slots 53 of a reinforcing plate 55 welded to the inner surface of bight 43. Sharp inner corners 57 are formed at the bend of each of the tabs 51 and pivotally support sharp projecting shoulders 59 of contact operating member 31. Each of the projecting shoulders 59 has a knife edge 63 which, when the shoulders 59 of the contact operating member 31 are mounted upon their mating tabs 51, extend into the slots 53 of the reinforcing plates 55 so as to pivot at sharp rear corners 57 of the mating tabs 51 to thereby provide a precise pivotal support for movement of the contact operating member 31 within the frame 5.

As can be seen from FIGURE 4, connected to the contact operating member 31 at the free end thereof is a contact operating means 119 which has a slot 121 cut in the lower portion thereof. The free end 22 of movable contact carrying arm 20 fits within the slot 121 and upon downward movement of the contact operating member 31, the condition responsive movable contact 21 is separated from the condition responsive fixed contact 19 to interrupt the electrical circuit controlled thereby.

Means are provided for actuating the contact operating member 31 and include an intermediate force transmission lever 64 spaced above the contact operating member 31 and in generally parallel relationship thereto. As is best seen from FIGURE 4, lever 64 includes body section 65 with an opening 67 therein, side flanges 69 which extend upwardly in a generally perpendicular fashion from opposite sides of body section 65, and a bearing shaft 71 which extends through aligned apertures formed in the front end of each side flange and is staked to these apertures to provide a pair of projecting trunnions 73. The axis of shaft 71 is generally parallel to the plane of body section 65 of lever 64. Oppositely disposed trunnions 73 are positioned in a pair of slots 75 which are formed in legs 33 of frame 5 adjacent the slots 45 to rotatably support levers 64. To readily position intermediate levers 64 upon frame 5 in a precise manner, a latch tab 81 is struck inwardly from one of the legs 41 and a slant reducing spring 83 is positioned upon the other leg. Latch tab 81 abuts one of the side flanges 69 to limit lateral movement of lever 64 toward leg 41 on which the tab is formed. Spring 83 includes an inwardly and downwardly extending leaf spring 89 and engages the adjacent flange 69 to resiliently limit lateral movement of lever 64 toward spring 83.

There is also provided a pair of raised oppositely disposed knife edges 91 spaced between the front and rear ends of the body section 65 which provide accurate pivots for a bearing 93. The knife edges 91 are configured cross-sectionally in the shape of an inverted V, and project transversely inwardly toward the center of opening 67 of the lever 64 to receive grooves 95 of the bearing 93. The grooves 95 are also in the configuration of an inverted V so that when the bearing 93 pivotally rests upon lever 64, distinct pivot locations for the bearing 93 are provided by the knife edges 91 of the lever 64. As shown in FIGURE 4, the bearing 93 also includes a pair of upper shoulders 97 within which aforementioned grooves 95 are formed, depending parallel pairs of struts 99 and a base 101. It should be noted that upper shoul- 4 ders 97 of bearing 93 sit above the knife edges 91 of lever 64.

An altitude adjusting screw 103 is provided for connection to the bearing 93 with a cup-shaped recess 105 being formed in the base 101 of bearing 93. The recess 105 has a slightly flattened annular sheet 107 upon which the conical shoulder portion of the altitude adjusting screw 103 rests so as to provide a force transmitting seat therefor. The primary function of the bearing 93 is to transmit the force difference between an altitude spring 111, to be discussed in greater detail hereinafter, and the condition responsive element, in this case a bellows 113, to the contact operating member 31 through the intermediate lever 64. As can be seen in FIGURE 3, altitude adjusting screw 103 provides a means for varying the bias on the condition responsive means 113.

In order to transmit a force from the condition responsive means 113 via the bearing 93 to the contact operating member 31 through lever 64, a projecting boss 115 has been formed on the undersurface of body section 65 adjacent a rear end 117 of the lever 64. A condition responsive force is thus transmitted from the bellows 113 to bearing 93 with the bearing 93 transmitting the difference between the force of the bellows and the altitude spring to knife edges 91 of lever 64. The intermediate lever 64 then pivots upon its trunnions 73, and projecting boss 115 of lever 64 engages an adjacent surface of contact operating member 31 near the shoulders 59 thereof to pivot the contact operating member 31 about its knife edges 63. By using a lever and the contact operating member 31 in this manner, it has been found possible to substantially multiply the movement of the free end or actuating end of the contact operating member to any condition responsive force.

In order to provide a continuously downward biasing force on the bearing 93, the altitude spring 111 transmits its compressive force to the screw 103 via a nut which is threaded thereto. By varying the compression of the altitude spring 111, the temperature range through which the switch operates may be predetermined. Specifically, the upper end of the altitude spring 111 encircles a downwardly extending flanged aperture 137 formed in a rigid cross bar 139 which is connected between the oppositely disposed legs 41. The altitude spring 111 is maintained in compression between the rigid cross-bar 139 and its threaded nut 135 and by adjustment of the screw 103, the compression of the altitude spring 111 is varied.

Means are provided for adjusting the desired response of the condition responsive contacts 19 and 21 and include a special cam follower assembly 147. The cam follower assembly includes an L-shaped cam follower 149 pivotally supported on bight 43 in the frame 5 and a bias spring 151 mounted in cantilever fashion upon the cam follower 149 and pivotally movable therewith. Cam follower 149 is-pivotally mounted to bight 43 by means of fingers 153 which are bent perpendicularly upward from the rear corners of the cam follower 149 and engage upper edges 155 of spaced slots 157 formed at the corners of the bight 43. Sharp inner edges of corners 159 are formed at the base of the fingers 153 and in order to provide a slight upward biasing of the inner edges 159 of fingers 153 against the upper edges 155 about which the cam follower pivots. A spring tab 161 is centrally spaced between slots 157 and is bent sligthly inwardly and outwardly from the bight 43 and engages a central nose 163 of cam follower 149 to provide a spring biasing force against a rear edge 165 of the cam follower 149 to provide a spring biasing force against a rear edge 165 of the cam follower 149. The nose 163 of cam follower 149 specifically engages and is biased by an inwardly extending shoulder portion 167 of the tab 161 and fingers 153 of the cam follower 149 extending upwardly from a base section 169.

An arm 171 extends outwardly from the forward edge 173 of one side of the cam follower base section 169 and is angled slightly upward therefrom. A free end 175 of the arm 171 has a generally conical boss 177 projecting upwardly therefrom which is responsive to the rotary positioning of a cam 178, to be discussed in detail hereinafter, to vary the pivotal position of cam follower 149. An eyelet 181 fastens one side of a supported end 179 of bias spring 151 to the cam follower, and one corner 183 of the bias spring 151 is attached to base section 169 by means of a rivet 185. Between the head of rivet 185 and the corner 183 of the bias spring 151, a range adjust washer 187 has been provided which is rotatably adjustable to vary the gradient of bias spring 151.

. A free end 193 of bias spring 151 is disposed directly above an adjust screw 197 which extends perpendicular upwardly from the central tongue 126 of the contact operating member 31 so as to be engageable with the free end 193 of the bias spring 151. The adjust screw 197 is threadably mounted within the contact operating member 31 and its relative position may be varied so as to adjust the range of the switch. When the switch 1 has been substantially assembled, adjust screw 197 is rotated into such position as to maintain a functional gap A with respect to the free end 193 of the bias spring 151 when the condition responsive contacts are in an open position and to continuously engage the free end of the biasing spring 151 when the condition responsive contacts are in the closed position.

Turning now to a discussion of the means for adjusting the size of the gap A, there is provided a rotatable cam 178 which is mounted on the underside of the cover plate 9 so as to engage the concial bump 177 on the cam follower 149. The follower 149 is thus pivotally responsive to the rotary position of the cam 178 and since the bias spring 151 is mounted in cantilever fashion upon the follower 149, the position of free end 193 may be pivotally altered by rotating the cam; thus, the size of the gap A may be varied. A sloping surface 178a of the cam 178 engages the conical bump 177 to pivotally vary the position of the free end of the bias spring 151. Most of the cam 178 is disposed within a circular recess 229 formed in a raised annulus 231 of cover plate 9 and in order to provide a limiting stop for the rotation of cam 178, a downwardly lanced portion 233 of the cover plate 9 extends slightly into the recess 229 to engage a lateral extension 235 of cam 178. It should be noted that the lateral extension 235 of cam 178 is also used to operate the manually actuable contacts; however, this will be described in detail hereafter. To facilitate manual rotation of the cam 178, a shaft 227 is connected thereto by suitable means.

Turning now to the condition responsive means assembly, there is provided a housing 241 in which the condition responsive means is contained. In this instance, the condition responsive means comprises a bellows 133 which contains a thermally responsive fluid such as methyl chloride or dichlorodifiuoromethane or other suitable source.

So that a temperature responsive actuating force is furnished for the switch 1, the bellows 113 is mounted within the housing 241. A restraining annulus having supporting arms 244 fitted into an annular groove in the inner wall of the bellows cup, restricts the upward movement of the bellows 113. To provide a transmitting area for the temperature responsive force, bellows 113 has a central, conically shaped recess 113A within which a smaller recess 113B is also contained. The smaller recess 113B receives the lower tip of altitude screw 103 and has an upwardly projecting nose centrally disposed therein which bears against the lower tip of the altitude screw. The altitude screw 103 also receives the downward biasing force of altitude spring 111 and transmits the difference of the forces between the spring 111 and the bellows 113 to hearing 93.

Turning now to the manually actuable portion of the switch 1, there is shown in FIGURE 5 means for operat- 6 ing the manually actuable contacts. Specifically, this means comprises a generally L-shaped actuator 300 which has a projecting boss 302 at its upper end for cooperation with the lateral extension 235 of cam 178 for operation thereof and which has a lower lip portion 304 which fits within a slot on the movable contact carrying arm 24 so that upon depression of the actuator 300, the movable contact 25 is separated from its normally closed engagement with the fixed contact 23 thereby opening an electrical circuit. The actuator 300 fits almost wholly within a recess 18 of the insulating housing 3 and lateral movement of the actuator 300 is precluded as the actuator 300 has an enlarged central portion 306 which engages the side walls of the housing recess for positive location there in. Longitudinal movement of the actuator is precluded by the bearing shaft 71 which is disposed adjacent the actuator and upon a small amount of rearward movement, the actuator 300 will abut the bearing shaft 71 to preclude further rearward movement thereof. By utiliz ing a lip and slot connection of the actuator 300 to the movable contact 25, the actuator 300 is positively held in the switch housing. This also precludes the possibility that the actuator 300 might fall out of the switch housing during the assembly thereof as might occur if it were not positively located therein. Turning now to the operation of the switch 1 and assuming first that the switch is utilized in a refrigeration machine for controlling the energization of a compressor unit, and further assuming that the temperature of the cold control is such that the condition responsive contacts are closed and the compressor motor is thus energized, the bias force of toggle spring 27 urges the contact operating member 31 upward to maintain the condition responsive contacts 19 and 21 closed. Consequently, the compressor will be operating to cause the temperature in the refrigeration machine to decrease and thus the temperature responsive fluid contained in the bellows 113 will decrease the internal pressure thereon so that the bellows will contract and as a result thereof, the force of the toggle spring 27 will be overcome and the contact operating member 31 will be snapped downward to its lower position whereby the condition responsive contacts will open and thus the circuit to the compressor motor will be interrupted.

For a more thorough and exacting description of the operation of the condition responsive portion of the switch, reference is made to U.S. Patent 3,096,419- Howell which is also assigned to the assignee of the present invention.

Referring now to the operation of the manually actuable contacts, it can be seen from the previous discussion that rotation of the cam 178 varies the bias of spring 151 against screw 197 and thus the condition level at which switch contacts 19 and 21 are operated is varied. It can be seen that further rotation of the cam 178 causes the lateral extension 235 to engage the projecting boss 302 of actuator 300. The extension 235 engages the sloped surface 308 of the actuator 300 and any force applied to this surface causes the actuator 300 to be depressed whereby the manually responsive contacts 23 and 25 are separated. In this manner, the single control shaft 227 is used for both setting the condition level at which the condition responsive contacts respond and actuating the manually actuable contacts.

In the embodiment just described, it is noted that the condition responsive contacts 19 and 21 are not directly operated by manual operation of the switch. However, if it is desired to turn oh the compressor while at the same time keeping the fan energized, such as would be desirable in an air conditioner, the condition responsive contacts 19 and 21 could still be used to control the energization of the compressor and the manually actuable contacts used for cont-rolling the energization of the fan. Reference is made to FIGURES 5 and 6 wherein there is shown another embodiment of the present invention which permits manual operation of the condition responsive contacts upon a predetermined degree of rotation of the control shaft 227 and upon further rotation of the control shaft 227, the manually actuable contacts are operated.

In this embodiment there is shown a reverse bent upstanding extension 38 connected to or integral with the contact operating member 31 which is disposed opposite means 119 and which is engageable by a bent back projection on a resilient arm 40. The resilient arm 40 is generally a leaf spring which has one end slidably mounted on the cover assembly 9 and has its free end 44 positioned above the reverse bent upstanding extension 38 of the contact operating member 31 for cooperating therewith. An operating knob 42 is attached to the leaf spring 40 and is used for controlling the longitudinal movement thereof whereby the bent back projection 44 is pushed into or pulled out of the path of the cam extension 235.

With knob 42 in the forward position so that the bent back projection 44 of the leaf spring 40 is in the path of the cam extension 235, rotation of shaft 227 causes cam extension 235 to engage the projection 44 of the leaf spring 40 and causes it to be pushed against the upstanding leg 38 which in turn causes the contact operating member 31 to be pushed downward against the biasv of toggle spring 27 and thus operate the condition responsive contacts 19 and 21. Upon further rotation of the shaft 227, the cam extension 235 engages the actuator 300 as previously discussed to operate the manually actuable contacts 23 and 25.

While the previous embodiments of the present invention have shown rotational means for controlling operation of the switch, it is possible to operate the switch with a push-pull action as can be seen by FIGURE 7. Specifically, the switch is modified so that the manually actuable contacts 23 and 25 are operated by a push-pull action instead of a rotational movement. The upper portion of the actuator 300 has been redesigned so that there is in one side thereof a notch 310 in which the cam 178 rides. It should be noted that cam 178 does not touch the walls of the notch 310 but is freely rotatable therein. As cam extension 235 is no longer necessary, it is omitted. A slidable sleeve 241 fits over shaft 227 and is adapted to engage an intermediate force transmission member 229, pivotally attached to the switch housing, which in turn engages the upper end 302 of the actuator 300. When sleeve 241 is pushed inwardly, it engages member 229 to force the member 229 against the actuator 300; thus forcing the actuator 300 down and moving the manually actuable contacts 23 and 25 from their first position to their second position.

Note that in each of the embodiments discussed the manually actuable switch contacts could be normally open rather than normally closed, thus upon operation thereof be moved to a normally closed position.

Thus, it can be seen that with the present invention there is provided internally in the switch a pair of condition responsive contacts and a pair of manually actuable contacts. Further, both pairs of contacts are controlled by the same control member.

While I have shown and described preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the present invention in its broader aspect and therefore it is the intention of the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the present invention.

What I caim as new and desire to secure by Letters Patent of the United States is:

1. An electric switch comprising: an insulated housing, a first pair of contacts disposed within said housing, means for moving said contacts between a first and a second position, condition responsive means connected to said moving means for controlling the movement thereof, means in engagement with said moving means for biasing said contacts in the first position, rotatable means for selectively varying the condition at which the first pair of contacts are moved toward the second position, a second pair of contacts disposed within said housing, one of said contacts being movable between a first open and a second closed position, an actuator connected to the movable one of said second pair of contacts, cam means connected to said rotatable selectively varying means for controlling said actuator such that movement of said selectively varying means also actuates a second pair of contacts.

2. An electric switch as described in claim 1 wherein; said insulated housing has a recess therein, said movable one of said second pair of contacts is mounted on a contact carrier having a slot therein, said actuator fits within said recess and has a lip at its lower portion which fits within said slot for engagement therewith, and said cam means engages said actuator at its upper end for control thereof.

3. An electric switch as described in claim 1 further including means engageable with an upstanding projection on said contact moving means for operating said first pair of contacts from the first to the second position, said means actuated by said cam means prior to said cam means actuating said second pair of contacts.

4. An electric switch as described in claim 3 wherein said last mentioned means comprises a resilient elongated leaf spring engageable with a reverse bent upstanding projection on said contact moving means to cause movement thereof.

5. An electric switch comprising: an insulated housing, a first pair of contacts disposed within said housing, means for moving said contacts between a first and a second position, condition responsive means connected to said moving means for controlling the movement thereof, means in engagement with said moving means for biasing said contacts in the first position, rotatable means for selectively varying the condition at which the first pair of contacts are moved toward the second position, a second pair of contacts disposed within said housing, one of said contacts being movable between a first open and a second closed position, an actuator connected to the movable one of said second pair of contacts, a force transmitting means pivotally mounted on said switch and engaging actuator for controlling the movement thereof, a shaft connected to said rotatable means for controlling rotation thereof, and a sleeve slidably mounted over said shaft which engages said force transmitting means to operate said actuator and cause movement of said second pair of contacts.

References Cited by the Examiner UNITED STATES PATENTS 2,833,895 5/1958 Weber et .al. 200- 2,853,583 9/1958 Rauh 200140 3,096,419 7/ 1963 Howell 200-140 3,103,568 9/1963 Liebermann et al. 200-140 3,178,539 4/1965 Crawford et a1 200-140 BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner. 

1. AN ELECTRIC SWITCH COMPRISING: AN INSULATED HOUSING, A FIRST PAIR OF CONTACTS DISPOSED WITHIN SAID HOUSING, MEANS FOR MOVING SAID CONTACTS BETWEEN A FIRST AND A SECOND POSITION, CONDITION RESPONSIVE MEANS CONNECTED TO SAID MOVING MEANS FOR CONTROLLING THE MOVEMENT THEREOF, MEANS IN ENGAGEMENT WITH SAID MOVING MEANS FOR BIASING SAID CONTACTS IN THE FIRST POSITION, ROTATABLE MEANS FOR SELECTIVELY VARYING THE CONDITION AT WHICH THE FIRST PAIR OF CONTACTS ARE MOVED TOWARD THE SECOND POSITION, A SECOND PAIR OF CONTACTS DISPOSED WITHIN SAID HOUSING, ONE OF SAID CONTACTS BEING MOVABLE BETWEEN A FIRST OPEN AND A SECOND CLOSED POSITION, AN ACTUATOR CONNECTED TO THE MOVABLE ONE OF SAID SECOND PAIR OF CONTACTS, CAM MEANS CONNECTED TO SAID ROTATABLE SELECTIVELY VARYING MEANS FOR CONTROLLING SAID ACTUATOR SUCH THAT MOVEMENT OF SAID SELECTIVELY VARYING MEANS ALSO ACTUATES A SECOND PAIR OF CONTACTS. 